True. A protein becomes functional only when it reaches its tertiary shape (3D). It is not necessary for the protein to reach the quaternary stage, but that is just a more complex functioning protein. It really is just two tertiary merged together. Example is red blood cells.
The half-life of a radioisotope is the amon the symbol 42He, the subscript 2 is the mass number for helium and the superscript 4 is the atomic number for helium.
There are several different processes, including glycolysis and the Calvin Cycle, but the umbrella term for getting energy from glucose is cellular respiration.
What system are we talking about? Context is needed... water cycle, cells, etc?